Automatic signal receiving system



Oct. 6, 1936. p LQWELL 2,056,200

AUTOMATIC SIGNAL RECEIVING SYSTEM Filed June 19, 1935 2 Sheets-Sheet 1 2 i PL'RC/VAL 0. LOWELL 06:. s, 1936. P. D. LOWELL 2,056,200

AUTOMATIC SIGNAL RECEIVING SYSTEM Filed June 19, 1935 v 2 Sheets-Sheet 2 PERC/ VAL D. LOWELL I Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE AUTOMATIC SIGNAL RECEIVING SYSTEM Percival D. Lowell, Chevy Chase, Md. I

Application June 19, 1935, Serial No. 27,437

11 Claims.

My invention relates broadly to radio receiving systems, and more particularly to a superheterodyne type of receiver having means for varying the frequency response of the receiver continuously over a predetermined frequency band, and means for automatically arresting the operation of said means under conditions of resonance of the receiver with an incoming signal wave.

One of the objects of my invention is to provide means for varying a tuning element in a signal receiving system over a predetermined frequency range and control means for arresting the operation of said means when a signal is incident upon the receiving system within the said frequency range.

Another object of my invention is to provide a construction of control means for a continuously variable tuning element which is simple, rugged and entirely automatic, and operative to effect instantaneous control of the driving means connected with the variable tuning element.

Still another object of my invention is to provide an emcient arrangement of filter means in cooperation with a beat frequency oscillator whereby actuating current will flow to a control device through said filter only at extremely low values of the beat frequency.

A further object of my invention is to provide motor driving means operative directly by a source of power and control means actuated by an increase in current due to reception of a signal, for arresting the operation of the motor driving means.

A still further object of my invention is to provide motor driving means operative by means which normally supplies current to said motor; and to effect control of the motor by a decrease in said current due to reception of a signal, whereby the operation of the motor is arrested.

Other and further objects of my invention reside in the circuits and arrangements hereinafter more fully described with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram showing one form of my invention in which a type of electromagnetic motor is employed as the driving means with a relay in the control circuit; Figure 2 is a portion of a similar diagram showing a magnetostriction type of motor drive energized directly from the control circuit; Fig. 3 shows a magnetic vibration type of motor which may be employed in place of the magnetostriction motor shown in Fig. 2 in the system of my invention; and Fig. 4 shows a piezo-electric type of motor which may likewise be substituted for the masnetostrictive motor shown in Fig. 2.

The system of my invention is especially useful where intermittent or occasional radio signals, having different frequencies within a cer- 5 tain band of frequencies, are transmitted on predetermined schedules, such as, for instance at aeronautical ground stations which pick up frequent radio telephone calls from aircraft which operate at different frequencies within a given in frequency band. If a radio signal is picked up at any point within the given band, the mechanical tuning is automatically and instantly arrested and the station received. When the station's carrier wave is cut off, or its frequency 15 changed, the arresting mechanism is released automatically and the mechanical tuning, or traversing of the frequency band, is resumed until a carrier wave of a frequency within the band is again received, whereupon the arresting opera- 20 tion is repeated.

This system permits of rapid traversal of the frequency band, and substantially instant arresting of the mechanism upon the reception of a radio telephone carrier wave within a few 'cycles of exact resonance.

The operation is accomplished by means of a variable condenser, rotated continuously by a motor, and connected across the tuned circuit of the frequency converting oscillator of a superheterodyne receiver. Thus, by rotating the plates of the condenser, the frequency response of the receiver is continuously varied over a band of frequencies, the limits of which are determined by the capacity of the varying condenser and the selectivity of the high frequency portion of the receiver.

A beat frequency oscillator is provided to produce a beat note of audio -frequency when a continuous wave, such as a radio telephone carrier, is being converted by the variable frequency oscillator to the intermediate frequency of the receiver. This current of audio frequency is fed though a "low-pass filter which will conduct only frequencies of, say, zero to 300 cycles. Thus, as the tuning condenser is rotated and a. continuous wave is intercepted, a. beat frequency will be produced having a pitch first above audible frequency, then rapidly decreasing into the audi- 'ble range until it reaches such a frequency as will pass through the low-pass filter. When this occurs, the low frequency beat note from the output of the filter is converted by a rectifier into direct current which is employed to alter the bias on the grid electrode of a gaseous type, relay electron tube causing a substantial change in the plate current thereof. In the arrangement shown. in Fig. 1, this current fiows through a relay winding which causes one set of contacts to open and another set to close, disconnecting the source of power from the driving motor in the former instance, and applying braking means for instantly arresting its rotation in the latter. when the carrier wave is cut oil, the beat frequency stops and the relay returns to normal, permitting the driving motor, and consequently the tuning condenser, to resume rotation.

In order that the signals may be heard without interference by the audio frequency beat note, two channels are provided in the receiver of my invention, connected subsequent to the first detector. One channel comprising a second detector and audio amplifier connects directly to" the telephone receivers or loud speaker. The other channel, comprising a screened grid intermediate frequency amplifier, a beat frequency oscillator in which the carrier wave at the intermediate frequency is one of the component oscillations, and an audio frequency amplifier, connects to the motor control circuit. The screened grid intermediate frequency amplifier prevents energy from the beat frequency oscillator from being conducted back through the second detector of the first or signal channel where it would interfere with the signals.

The driving motor shown in Fig. l is of the induction motor type. and braking action is obtained by applying a direct current to its field winding when the alternating driving current is removed. A more suitable motor is the magnetostriction type shown in'Fig. 2 which will stop more quickly without braking means when the exciting current is removed. Also, the motor shown in Fig. 2 is operated directly from the energy in the plate circuit of the gaseous relay tube, thereby making it unnecessary to use a relay device, and consequently permitting a shorter time interval to elapse between the reception of the beat frequency and the stopping of the rotation of the tuning condenser.

Referring to the drawings, in more detail, reference character I represents an antenna of the doublet type; 2, a transmission line cable; 3, a pair of variable resistors in series with the line; 4, a variable center tap resistor across the line; and 5, a shielded radio frequency coupling transformer connected to the input circuit, 6, of the receiver. The purpose of the resistors I and 4 and the transformer 5 is to provide a perfect balance of the transmission line andantenna, thereby reducing the pickup of man-made noises and local electrical disturbances.

The superheterodyne receiver is represented as having an input circuit 8,.first detector I, frequency converting oscillator 8, intermediate frequencycircuit 9, second detector audio amplifier ii, and output circuit l2 to which is connected head telephones or a loud speaker. This represents only in a broad manner the primary circuits of this type of receiver.

Auxiliary tuning condenser 21 is connected in shunt with the main tuning condenser of the oscillator 8 and is continuously rotated by motor 26. Motor 26 as shown in Fig. 1 comprises an armature, 28, connected with the shaft of the condenser 21, and a field winding, 25, mounted on the core structure 29.

The input of the screened grid-intermediate denser III which will pass the radio frequency carrier currents to the intermediate frequency amplifier. The screen grid "a in amplifier i2 is provided for the purpose of screening the grid |2b from the plate iIc, thereby preventing energy from beat frequency oscillator II from feeding back into the second detector ill through the tube II, which would cause an undesirable'beat note to be heard in the aural output |2. An intermediate frequency transformer i4 couples the output of amplifier It to another second detector or converter stage ll. Beat frequency oscillator is is also coupled to the second detector l5, and

a heterodyne note is produced when a continuous wave carrier is received. The output of the second detector it is connected with an audio frequency amplifier It, the output of which is fed into a low pass filter network I! through the output circuit II.

The filter It is designed to pass currents of frequencies less than 300 cycles, so that as the tuning of the receiver comes within 300 cycles of exact resonance with the carrier, current is passed by the filter "and the controlapparatus begins to function, whereby the continuous tuning is stopped substantially at true resonance due to the instant of time delay in the operating means.

The output of the filter is converted to direct current by a full wave rectifier 20 and its associated circuits. A gaseous relay tube 2| is operated from alternating current, having the plate voltage and grid bias therefor supplied from the secondary of power transformer 22. Fig. 1 shows the winding 22 of an electromagnetic re-' lay connected in the plate circuit of the relay tube 2|. The grid and plate voltages of tube 2| are polarized, in the arrangement shown in Fig. l, in such a-manner that when the plate is positive, the grid is negative; and, by means of the potientiometer 32, the grid bias is adjusted negatively so that normally, with no signal, the plate current is zero. The output of the rectifier 20 is so connected to the relay tube 2| that when a signal is received, and current of beat frequency is passed by the filter l9 and rectified by tube 20, a positive potential is applied to the grid of relay tube 2|, counteracting the normal negative grid bias sufilciently to cause the relay tube 2| to arc, and draw a large plate current. Due to the natural rectifying action of relay tube 2|, the plate current thereof is half wave rectified and operates relay 23 and contacts 24. As shown in Fig. 1, these contacts remove the alterating driving voltage from the field winding 25 of motor 2i and connect thereto a source of direct voltage, shown as a battery 2|, thereby causing a braking action which effects instantaneous stoppage of the motor 26. Immediately upon the interruption of the incoming carrier current, the beat frequency is destroyed, the positive potential on the grid of the relay tube 2| is removed and the relay contacts 24 return to normal, connecting the driving voltage to the motor 26, whereby the continuous traversal of the frequency range of the receiver is resumed.

Fig. 2 shows the use of a magneto-striction type of motor 22, which comprises a winding 35 and a magnetostrictive core member 26 carrying a pawl 31 cooperatingwith ratchet wheel 38 for driving the variable condenser 21. The winding 35 is energized directly from the plate circuit of relay tube 2| by the voltage across. plate resistor 34,- the pulsating plate current of tube 2| being sufilcient to drive the motor. In the arrangement shown in Fig. 2, relay tube 2i is encountered and the control circuits are again normally draws plate current when the plate is positive so that the motor will operate continuously. The grid of relay tube ii is normally biased to an amount which will permit sufficient plate current to flow; and the output from the rectifier 20' is reversed as compared with the connections in Fig. 1, so that an incoming signal will cause a negative potential to be put on the grid of relay tube 2i, cutting oi! the plate current and causing the motor to stop. Interruption of the carrier removes the negative potential on the grid of the relay tube 2| and permits the resumption of operation of the motor.

Other types of motors adaptable to operation directly by the plate current of the tube 2i may be employed in place of the magnetostriction motor 32. A magnetic-vibration motor of the type shown in Fig. 3 or a piezo-electric motor such as shown in Fig. 4 may be employed instead of the magnetostriction motor 32 shown in Fig. 2. The magnetic-vibration motor comprises a pair of field electro-magnets 38 and 39, wound in opposite directions, and a permanently polarized armature 40 mounted adjacent the field magnets and carrying pa'wls 4| and 42 cooperating with ratchet wheel 43 for driving the variable condenser 21. The piezo-electric motor comprises the vibratable crystal 44 mounted between electrodes 45 and 45. Electrode 45 is arranged to vibrate in unison with crystal 44, and has fixed to it a pawl 46 which cooperates with a ratchet wheel 47 to drive the variable condenser 21 when the crystal 44 and electrode 45 vibrate.

Reviewing the operation of the circuit, rotating condenser 21 continuously varies the tuning of the superheterodyne receiver. Phones or speaker are connected in the output circuit and normal signals or speech are received, without interference from the beat note, whenever the receiver is tuned to a signal, automatic means being operative to stop the rotation of the tuning condenser.

From the input of the second detector of the superheterodyne receiver, a portion of the signal energy is diverted to the motor control circuits which comprise a screened grid intermediate frequency amplifier, a beat frequency oscillator and another second detector or converter stage. The audio beat frequency output of the 50 converter stage is amplified, and filtered so that only low beat frequencies will pass into the rectifier and relay tube causing the motor stopping mechanism to operate with precision.

The low pass filter serves to delay the stopping of the motor until the receiver is substantially resonant to the carrier wave received, or in other words, the motor will stop when the beat frequency has reached a value very near zero. Thus the station will be properly and accurately "tuned in at the instant the rotating condenser is stopped.

It has been found from tests that the tuning condenser can rotate at a speed of about one revolution per second, covering a frequency band of plus or minus 20 kilocycles and still be stopped within 300 cycles of zero heat, which is as accurate as, if not more so than was possible under the practice of manual tuning heretofore nec- 70 essary, and which permits reception of a voice carrier without appreciable distortion. When the carrier wave is interrupted or cut off, the potential on the grid of tube 2| reverts immediately to normal, causing the motor to resume rotation of 75 the tuning condenser until another carrier wave operated to stop the motor.

While I have described my invention in certain preferred embodiments, I desire it to be understood that modifications may be made therein, and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. An automatic radio frequency signal receiving system comprising means for continuously varying the frequency response of said signal receiving system, a beat frequency oscillator comprising means for combining an oscillation derived from a continuous wave oscillation received by said receiving system and an independently generated oscillation, a low-pass filter system connected with the output of said beat frequency oscillator, and control means actuated by the output of said filter system for automatically controlling the operation of said first mentioned means.

2. An automatic radio frequency signal receiving system comprising mechanical means for continuously varying a tuning element in said receiving system, control means for stopping the operation of said mechanical means upon resonance of said receiving system with an incoming continuous wave, and means whereby said control means are energized prior to the condition of exact resonance whereby said mechanical means may be stopped substantially at the condition of resonance regardless of the time element of said mechanical means.

3. An automatic radio frequency signal receiving system comprising means for continuously varying the frequency response of said signal receiving system, and means for controlling the operation of said first mentioned means; said control means including a beat frequency oscillator having zero beat output at the condition of resonance of said receiving circuit with an incoming oscillation, and a low-pass filter system adapted to pass a bandof frequencies adjacent zero whereby a beat frequency not zero may be employed to actuate said control means prior to the condition of resonance in order that said first mentioned means may be stopped substantially at the condition of resonance.

4. The method of automatically receiving radio frequency signal energy within a given band of carrier frequencies which comprises continually varying the frequency response of the receiver over the given frequency range, independently generating an oscillation and causing this oscillation to beat with an oscillation derived from an incoming continuous wave at a frequency approaching zero, filtering the beat frequency thus produced and allowing only frequencies adjacent zero to pass, and employing currents of the highest frequency passed in said filtering stage to control the operation of varying the frequency response of the receiver.

5. In a superheterodyne type of radio frequency signal receiving system, the method of automatically receiving signal energy within the frequency range of the receiver which comprises continuously varying the frequency response of the receiver, independently generating an oscillation and causing this oscillation to beat with an oscillation of the frequency at the intermediate stage of the superheterodyne system derived from an incoming continuous wave. the beat thus produced being of audio frequency and approaching zero as 'the'oscillation derived from the incoming wave approaches the intermediate frequency of the system, filtering the beat frequency and allowing only frequencies adjacent zero to pass, and employing currents of the highest frequency passed in said filtering stage to conate frequency of said system, means for combin-- ing the output of said oscillator and the intermediate frequency oscillations in said superheterodyne receiving system, a low-pass filter connected with-the output of said combining means and operative to pass frequencies adjacent zero, and control means connected with the output of said filter and initially actuated by currents of the highest frequency passed by said filter whereby said control means is operative to stop the said means for varying the frequency response of the receiver substantially at the condition of resonance, takinginto consideration the time lag in the application of the control. a

7. In combination with a superheterodyn radio frequency signal receiving system having an input circuit, an oscillator, a converter or first detector, intermediate frequency circuits, second detector and audio frequency circuits, automatic signal receiving means comprising a variabletuningelement connected in said oscillator circuit, electromechanical means for continuously varying said tuning element; a connection from said intermediate frequency circuits to a beat frequency oscillator, audio frequency blocking means disposed in said connection, a low-pass filter system connected with the output of said beat frequencyoscillator; a gaseous type electron tube relay device including a control electrode, said relay device being adapted to control the operation of said electromechanical means; a rectifier device having input and output circuits connected respectively to the output of said filter system and to the control electrode of said relay device, the currents of beat frequency passed by said filter being rectified in said rectifier device and impressed on the control electrode of said relay device, whereby the current through said relay device is controlled by the current of beat frequency, of which the carrier current of the signal is one component, and the operation of said electromechanical means is controlled by the received signal.

8. In combination with a superheterodyne type of radio frequency signal receiving system, automatic signal receiving means comprising a variable tuning element in said receiving system. a motor mechanically connected with said tuning element for continuously varying said element, control means for said motor comprising an electromagnetic relay device having contacts normally closed for supplying power to said motor and normally open contacts adapted to connect braking means to said motor, actuating means for said electromagnetic relay device comprising a gaseous type electron tube relay device, said tube relay device being normally nonconductive, and means excited from the intermediate frequency circuits of said superheterodyne receiving system fofrendering said tube relay device conductive when said tuning means effects resonance in said receiving system with an incoming continuous wave, whereby said electromagnetic relay device is operated to remove power from said motor and to connect said braking means. i

9. In combination with a superheterodyne type of radio frequency signal receiving system, automatic signal receiving means comprising a variable tuning element in said receiving system, a magnctostrictive motive device mechanically connected with said tuning element for continuously varying said element, control means for said magnetostrictive device comprising a gaseous type electron tube relay device having its output connected with said magnetostrictive device, said tube relay device being normally conductive for energizing said magnetostrictive device, and means excited from the intermediate frequency circuits of said superheterodyne receiving system for rendering said tube relay device non-conductive when said tuning means effects resonance in said receiving system with an incoming continuous wave, the operation of said magnetostrictive device thereby being stopped.

10. Automatic signal receiving means as defined in claim 8 in which the means excited from the intermediate frequency circuits of the superheterodyne receiving system includes a beat frequency oscillator having one of the component frequencies thereof supplied through a connection to the intermediate frequency circuits of said receiving system, a low-pass filter system connected with the output of said oscillator and operative to pass only frequencies adjacent zero, a rectifier device connected with the output of said filter system andoperative to rectify the oscillations of beat frequency into direct current; a control electrode in the tube relay device, and means for impressing the positive potential from said rectifier device upon said control electrode whereby said tube relay device is rendered conductive.

11. Automatic signal receiving means as defined in claim 9 in which the means excited from the intermediate frequency circuits of the superheterodyne receiving system includes a beat frequency oscillator having one of the component frequencies thereof supplied through a connection to the intermediate frequency circuits of said receiving system, a low-pass filter system connected with the output of said oscillator and operative to pass only frequencies adjacent zero, a rectifier device connected with the output of said filter system and operative to rectify the oscillation of beat frequency into direct current; a control electrode in the tube relay device, and means for impressing the negative potential from said rectifier device upon said control electrode whereby said tube relay device is rendered nonconductive.

PERCIVAL D. LOWELL. 

